1. Field of the Invention
The present invention relates to systems and methods for performing refractive laser surgery on the eye, and, more particularly, to such systems and methods that process data for use as input for a system that adaptively modulates sensed data on the basis of data from prior procedures.
2. Description of Related Art
In a particular treatment system for calculating a laser ablation treatment profile for an eye to improve vision, a plurality of Hartmann-Shack measurements are collected, and the image of the resulting dot pattern is enhanced. The position of each dot is measured, and wavefront slope data are calculated from the dot centroids. The original wavefront is then reconstructed mathematically.
The results of these calculations for each of the plurality of measurements are then compared, and any “outliers” are removed. The remaining reconstructed wavefronts are combined to form a composite result, which is in turn used to define an ablation treatment profile. In addition, a “classical” prescription can be calculated from the composite result, which can be compared with the results of a phoropter measurement.
A clinician typically modifies the prescription entered into the treatment system. Such modifications are based upon prior experience with outcomes achieved with that particular treatment system, and also upon experience with particular patient populations derived from, for example, demographic data. For example, a surgeon might enter a 2-diopter myopic treatment prescription for a patient diagnosed with 3 diopters of myopia if analysis of previous outcomes indicates a 50% overcorrection using this system for patients of a particular category. Such an empirical alteration of entered treatment parameters based upon previous experience is referred to as a nomogram adjustment. Nomograms are considered essential by the ophthalmic community because different clinicians employ different surgical techniques, operate under different environmental conditions, have distinct patient demographics, etc.
Conventional surgery involves a limited number of well-defined treatment parameters, principally spherical error, astigmatic error, astigmatic axis, optical zone size, and blend zone size. Thus it is relatively straightforward for a surgeon to develop nomogram formulas based on conventional clinical examinations before and after surgical procedures. In contrast, wavefront-guided customized treatments, such as that disclosed in commonly owned U.S. Pat. No. 6,270,221 B1, the disclosure of which is incorporated herein by reference, involve complex a mathematical description of the pre-operative aberration profile, which is transferred electronically to the treatment system.
Although such a precise wavefront description can in theory be modified empirically to yield a better outcome, typically clinicians are not skilled in the analytic interpretations of these mathematical parameters. In addition, at present there is no known convenient method for a surgeon to modify a wavefront-based prescription prior to a procedure such as laser surgery.
In currently used wavefront-based treatments, the raw wavefront data are modulated to generate a treatment profile in order to account for an apparent radial dependence in the effectiveness of ablative treatment on the corneal tissue. This, however, is currently applied identically in all treatments.
The inventors of the present application have previously disclosed a system and method for creating a nomogram for adaptively modulating sensed wavefront data based upon prior treatment outcomes (U.S. Pat. No. 6,698,889, which is commonly owned herewith, and the contents of which are incorporated hereinto by reference).
Aberrometers known in the art can calculate and display on screen an effective clinical prescription from a wavefront profile. In most cases the wavefront-derived prescription is in good agreement with independent sphere/cylinder/axis data obtained via classical refraction. However, in some case the wavefront values are significantly different, and are perceived as incorrect. This most commonly occurs in post-operative cases, that is, examinations performed after the patient has had laser vision correction surgery. At present there exists no system to assess confidence in the final reported refraction estimate.
A dubious refraction reported by an aberrometer can erode physician confidence in the aberrometer's general performance. In addition, such a result can be indicative of a problem with the measurement, which could, for example, be remedied with a repeat measurement. An example of such an eventuality is if the patient's tear film is breaking up due to infrequent blinking. Furthermore, such questionable data should not be included in any automatic trend analysis as taught in the '889 patent for nomogram optimization.
There yet remains a need for refining the data that are used as input for the system and method described in the '889 patent and similar systems, and also for alerting a clinician if a calculated prescription is suboptimal.